B1 Buffer Preamp

lineup said:


Lineup - now waiting for the investigations and findings that Mr Pass will do in B2


Me 2 :)

I already started messing around with what may become known as B2 ;)

Ok, not exactly that, but...

I started with high-pass part of the circuit, because this is what I need for my Open baffle speakers. For the moment, no notch filter, only a 12 db/oct high-pass. I set it up at 80 Hz. (I've experimented with a broad range of frequencies, and between 80-100 Hz seems to work best). The C and R values are calculated using Rod Elliot's ESP calculator: http://sound.westhost.com/project81.htm
The high -pass circuit is very similar to the block that he is using in Project 81, except that the op-amp is replaced by Papa's Jfet buffer. Well, almost. The exception being the current source; since I don't have enough 2Sk170's handy (can't buy them locally), I have purchased some BF245C ones. (Thanks Choky) However, I have to use it with the resistor to set a proper current...
Also, I'll use a split supply, +-9 v for the moment (I am using two 9 V batteries), but If I use regulators, I may most probably use +-12 v (7812 and 7912 Ic regs).

Work in progres...If I am lucky, I may get it done over the weekend...
Will post pics...

P.s. Ot question for Papa: What alignment did you use for you 12 Db/oct high pass? You mentioned somewhere that you had to increase the Q of high-pass to get smoother response?...

Regards,

Vix
 
Originally posted by Zen Mod
just in case - look at Shunty schm for CCS with BF245C
----
measure first Idss of your 170 (at 9V)
then tweak that resistor for BF

I use plenty of BF245 for current sources (Not for real yet. But in Simulation)

Having a supply of BF245A, BF245B & the mentioned BF245C is well worth it for a JFET designer.
- BF245A at currents of like 1-3 mA
- BF245B at currents of like 4-5 mA
- BF245C at currents of >5 mA

These BF245 are good bargain and fairly low cost
compared to 'waste' 2SK170 and other Super priced JFET for the CCS job (costant current sources)

So, I say to anyone, follow Zen Mod good advice
.. and get yourself some home supply of BF245
to assist your other JFETs in circuit.


Lineup
 
Official Court Jester
Joined 2003
Paid Member
DVBjunky said:
Hi ZenMod,

so if i want to use the B1 in my Aleph J then your schmatic will work with these regulators?

Regulator LM317

Mini-Regulator


in both cases max input voltage is pretty close to voltage you have in Aleph J - just look at 25V markings on electrolyt caps on both regs you linked to.

anyway - bigger problem is that you can't use any of these for minus leg , because GND is already established on your main cap bank in A J .

if you made AJ , and you can make B1 , then you can make any adequate regs ........ either 317/337 , 7812/7912 or discrete zener followers ........ with pair of two small bjt darlingtons .

hehe - you can even make simple shunt regs with two darlingtons ...... just look somewhere in few Treshold NS10 threads for schematic
 
KSTR said:
No no, it's 13 Euros (US$20, today ;-) for a bag of 25pcs.
And they have 2SJ74 for EUR10, 10pcs., too.


MRupp said:


The text is obviously in German: the price is per lot of 25 pieces, plus shipment, so 0,67 euro or roughly 1 $ per JFET. I think that is not too bad, especially considering this is a well know local supplier and you still get the original and not any fakes, plus they have J74BL as well.


Patience please I'm a novice: I know that for Q100/101 etc I need 2SK170BL's (or alternatives) - do I also need 2SJ74's and J74BL's ?
 
Official Court Jester
Joined 2003
Paid Member
DVBjunky said:
Hi ZenMod,

so if i want to use the B1 in my Aleph J then your schmatic will work with these regulators?

Regulator LM317

Mini-Regulator


here it is - sweet & simple

use any smaller darlingtons , with Pd from 25W up
 

Attachments

  • chokys_darlington.jpg
    chokys_darlington.jpg
    27.1 KB · Views: 3,720
Hi,

I need a bit help with setting Idss...

First, I measured Idss on 170's, using 9 v battery and tying Source to Gate. One of them was 9.4 mA and the other one was 10 mA.
So, I decided that I should tweak the BF245C resistor to give me around 9mA (It was putting put 14.2 mA without resistor). But, here is the problem: I started with 2.2 K between Source and Gate, and got only 1.5 mA. So I decreased the reistor until I got 9 mA. Resistor value was 110 ohms! (2x220 in parallel). It this Ok? :scratch:

Thanks
 
Official Court Jester
Joined 2003
Paid Member
Vix said:
Hi,

I need a bit help with setting Idss...

First, I measured Idss on 170's, using 9 v battery and tying Source to Gate. One of them was 9.4 mA and the other one was 10 mA.
So, I decided that I should tweak the BF245C resistor to give me around 9mA (It was putting put 14.2 mA without resistor). But, here is the problem: I started with 2.2 K between Source and Gate, and got only 1.5 mA. So I decreased the reistor until I got 9 mA. Resistor value was 110 ohms! (2x220 in parallel). It this Ok? :scratch:

Thanks


why you have doubts in your own measures ?
maybe I mixed thing or two when I told you to start with 2k2 :rofl:

then that CCS string in my case was really for 1~2mA , not 5 :clown:
 
Member
Joined 2004
Paid Member
Official Court Jester
Joined 2003
Paid Member